With my extensive furkid family, I made 3 boxes all of wood and other scrap materials, and placed 2 of them in the bathroom and one next to the front door. I could purhcase cat litter, but instead, use sand, because there is plenty of that around here, and the "price is right". The boxes are large. The largest one is 38" long x 19" wide and 5" deep. It holds about 15 gallons of sand, and weighs too much to carry out of here, ( probably close to 100 + lbs). So, I put wheels on all of them with turnable front axle, with swivel castors on the other two, and a pull rope. 'System works well. They get dumped about every 2nd to 3rd day, and refilled with fresh sand.

........wayne